Very high intensity light source using a cathode ray tube



2 Sheets-Sheet 1 Filed July 51, 1961 INVENTOR. NORMAN F. FYLER ATTORNEYS June 15, 1965 FYLER 7 3,189,784

VERY HIGH INTENSITY LIGHT SOURCE USING A CATHODE RAY TUBE Filed July 31, 1961 2 Sheets-Sheet 2 74 76 START vAmAaLE SIGNAL DELAY, 54 GUN 2 SOURCE REGEN.

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REGEN. 78 CRT CATHODE LIGHT CAMERA HEATER SOURCE v SUPP'LY I DELAY, 5 g4. 8 cRT I ILIIII LIGHT I- CAMERA SOURCE CRT LIGHT Lilli .1, CAMERA SOURCE -l----- AIR HE A mm F86 3 I00 I00 no so In 2 10 2 Z 0- u 1 so 3 lz m so 0 g 40 I 9 u 30 J 2 g z 20 J U a no -ANG5TROMS INVENTOR.

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o BY TIME AFTER EXCITATION RW '15 nsuovso-mcao'sa'couos AT TOBN EYs 3,159,784 VERY HIGH INTENSITY LIGHT SOURCE USlNG A ATHODE RAY TUBE Norman F. Fyler, Menlo Park, (Ialif, assignor to Litton Precision Products, End, a corporation of Delaware Filed duty 31, 1961, Ser. No. 127,984 Ellaims. (Cl. 315-30) This invention relates to high intensity light sources for producing light pulses of relatively brief duration.

It has previously been proposed to employ strobing light sources for photographic and other purposes where brief high intensity illumination is desired. These light sources have generally been of the gaseous discharge type, and have been actuated by electrical triggering circuits; however, the time required for deionization of the gas is longer than would be desired for many purposes. In addition, the light intensity levels are much too low for a number of important applications.

Accordingly, a principal object of the present invention is to provide a light source which is much brighter and which lasts for a much shorter time period than the strobing light sources which have been employed heretofore.

In accordance with the present invention, this object is achieved through the use of a cathode ray tube having a faceplate coated with a phosphor having a relatively short persistency, and a cathode having a broad surface, area, of the same order of magnitude as the area of the faceplate. In addition, arrangements are provided for avoiding destruction of the phosphor by the heat from the broad area cathode which normally is literally red hot.

In order to focus electrons onto the faceplate, the cathode is preferably concave, of the Pierce cathode type or of other concave form. A grid is provided to control the application of brief pulses of a high intensity electron beam to the phosphor coating.

The invention generally contemplates the use of cathode ray tubes having a screen of appreciable size, at least one inch square or about six square centimeters, for example, and much larger screens may be employed. In addition, instead of the usual pencil electron beam which is used continuously, the screen of the cathode ray tube is saturated with an electron beam of high density and high intensity. Thus, for example, it is contemplated that at least 5, and preferably to 50 or more, amperes of electron beam current be applied to each square centimeter of the cathode ray tube screen. A phosphor having a relatively short persistency, for example, one which requires only 0.02 microsecond or nanoseconds (where a nanosecond is 10 seconds) for light to decay to less than one-half its maximum brightness, may be employed.

Where electron beam pulse lengths of 10 to 20 nanoseconds are employed, the total duration of the emitted pulse of light will be less than nanoseconds, or less than one twenty-fifth of a microsecond. This is in contrast to the prior art gas discharge strobe lights which normally last for more than one microsecond.

With regard to useful light intensity, when a six-inch aluminized screen is employed, with about 2,000 amperes of current in a 10 to 20 nanosecond pulse, the peak light intensity is the radiafiant energy equivalent of at least a billion lumens, in the near ultraviolet spectral range. Furthermore, the spectral distribution of the phosphor may be matched to the utilization device, such as the 6 photographic film which may be used, or may be centered in the visible range, so that all the light output may be used. To compare the present light source with other known sources of light, the usable light of a one hundred watt light bulb in the spectral range in question is only about one-millionth that of the present light source.

i fl Patented June 15, 1965 Furthermore, even the more intense light of the gaseous light sources having emitting areas comparable to the present light source are at least one hundred times less bright than the present light source.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of construction and operation, together with further objects and advantages thereof, will be better understood from the following description considered in con.- nection with the accompanying drawing in which an illustrative embodiment of the invention is disclosed, by way of example. It is to be expressly understood, however, that the drawing is for the purposes of illustration and description only and does not constitute a limitation of the invention.

In the drawing:

FIG. 1 is a cross-sectional view of a high intensity light source in accordance with the present invention;

FIG. 2 is a schematic drawing of a system employing the cathode ray tube light source of the present invention; and

FIGS. 3 and 4 are plots which show the spectral distribution and the decay curves, respectively, of a typical phosphor which may be used in the device of FIG. 1.

With reference to the drawing, the high intensity light source includes an outer vacuum-tight envelope including a glass cylinder 12, a metal housing 14 for the cathode assembly, and the faceplate 16. In addition to these major portions of the vacuum tube envelope, various sealing elements are also provided.

The three major electrodes include the cathode 18, a wire mesh grid 20, and the anode which includes the large cylindrical member 22 connected to the aluminized coating on the inner surface of the faceplate 16. The cathode 18 includes a broad area emissive surface, and is of the Pierce type. The wire mesh grid 20 generally follows the surface of the cathode 18. In practice, the beam of electrons from the cathode 13 is substantially selffocusing and does not need the strong axial magnetic field which is often employed in beam type tubes. However, some axial magnetic field focusing may be employed, if desirable.

A principal feature of the invention is the use of a cathode which is capable of saturating a broad area phos phor screen. Thus, for example, the 5" cathode 18 provides pulses of up to 2,000 amperes of current. This will provide current density on the phosphor screen 24 of ten or more amperes per square centimeter. It is through the use of these high levels of current on the phosphor screen that the phenomenally high levels of illumination noted above may be achieved.

The geometry of the tube of FIG. 1 is determined in large measure by the presence of the broad area cathode 18. This cathode 18 is red hot when the tube is in operation. This means that it is at a temperature of about 850 degrees to 900 degrees centigrade. The phosphor screen 24 on the inner surface of the faceplate 16 can only withstand temperatures of approximately 600 degrees Centigrade. Accordingly, it is advantageously spaced by a considerable distance from the cathode 18; in addition, it may be cooled by the passage of cooling fluids over its outer surface.

It may also be noted that the anode cylinder 22 is mounted from the screen end of the tube, the cathode 18 is mounted on the stem 26 from the cathode end of the tube, and the grid structure 20 is mounted on a centrally located supporting structure including the metal ring members 28, 30 and 32, as shown in FIG. 1. In practice, the cold spacing of the grid 20 from the cathode 18 is approximately mils. As the cathode heats up, how ever, the stem 26 expands as a result of the intense heat of the cathode 18, and the spacing between the cathode 31% and the grid 20 is reduced to about 60 or 70 mils.

For completeness of description, cetrain other components of the tube should be discussed. Thus, for example, the tube electrodes are provided with corona rings 34, 36 and 38 to prevent undue arcing within the tube structure. These rings are required because of the high anode accelerating voltages which are employed. These may be in the order of 60 kilovolts, for example, depending on many tube parameters. With regard to the grid potentials, the grid is normally biased negative by about 50 or 100 volts and is puised positivelyto a Voltage of 5 to 10 kilovolts. The corona rings mentioned above include the rolled edge 34 on th grid supporting member 32 and the ring 36 on the lip of the cylinder 22 toward the grid structure. In addition, the grid supporting frame is provided with a smoothly rounded surface 38 facing the anode member. The narrow glass cylinder 40 is employed to isolate the grid supporting elements from the cathode assembly 1d. The resistance wires 42 which are mounted immediately be hind the cathode is are provided with current through the stem 26.

Anode voltages are supplied to the metal flange 44 which is connected to the anode cylinder 22. Portions of the composite assembly 44 are also sealed to the faceplate 16 and to the glass cylinder 12. Suitable metal elements 46 and 4-8 are employed to support gettering material which is flashed following assembly and evacuation of the tube of FIG. 1.

The phosphor screen 2 on the inner surface of the faceplate i6 is of a carefully designed form. Thus, the faceplate is initially coated with a layer of a phosphor having the desired spectral response and short persistency. One typical phosphor which may be employed is available commercially under the designation IETEC Phosphor No. Pl6. As indicated in FIGS. 3 and 4, the spectral response of the phosphor peaks up at about 3800 Angstroms and extends over a spectral range from about 3500 Angstroms to about 4300 Angstroms.

FIG. 4 shows the decay curve for the phosphor mentioned above. It may be particularly noted from the plot of FIG. 4 that the brightness decays to one half of, its maximum value within 0.02 microsecond, or 20 nan0 seconds, following the cessation of the impinging electron beam.

In addition to a phosphor having the desired spectral response and short persistency characteristics, the inner surface of the faceplate 16 may be aluminized. This technique is well-known and is employed in the teler vision tube field, for example. However, it is'particularly important in the present case to obtain a good electrical connection between the inner aluminized coating on the faceplate 16 and'the remainder of the anode structure. Specifically, the faceplate must be entirely at the high anode voltage to avoid diffusion of the electron beam. With the high beam intensities which are employed in the present device, a significant separation of the beam by electrostatic forces would occur in the absence of a strong and uniform anode field directing the electrons toward the phosphor coated faceplate 16.

The cathode ray tube light source of FIG. 1 may, for example, be used in systems such as that of FIG. 2. The system of FIG. 2 is a photographic arrangement for obtaining high speed snapshots of a projectile 52 shot from a launching mechanism such as the gun 54; A series of cathode ray tube light sources 56, 58, and 6% may be provided. Suitable cameras 62, 64 and 66 are mounted opposite the light sources 56, 58, 60, respectively. Suitable light baffles (not shown) may be provided to prevent the transmission of light from the light source 56 to the cameras 64 or 65 and to similarly restrict the light from other light sources. Forced air may be directed to the faceplate of each of the three cathode ray tube light sources by a suitable duct 68. Voltage may be supplied Cir to the anode structure of each of the tubes from the high voltage power supply 79. Similarly, heater current is supplied to each of the units by the power supply 72.

The enabling signals to the grids may be accomplished by the use of a timing control circuit including the source of triggering pulses 74 and a series of delay units 76, 73 and 8%. Each of the delay circuits 76, 78 and 89 may also include a regenerative amplifier for providing the high voltage signals required for energization of the grids of each of the cathode ray tubes. With the delay circuits 76, 7S, and 8t being properly proportioned for synchronism with the speed of the projectile 52, the light source 56 will be triggered while the projectile 52 is directly between the camera 62 and the light source 56. Similarly, the light sources 58 and 6t will'be triggered in sequence to photograph the projectile 52 as it is before their faceplates. In passing, it may also be noted that the duct 68 may be located below the cathode ray tube 56, 58 and 6d, and may be directed upwardly toward the faceplatcs of the tubes. In this way the duct does not interfere with the transmission of light from the light sources past the projectile 52 to the cameras.

It is to be understood that the above-described arrangements are illustrative of the application of the principles f the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention. Thus, by way of example and not of limitation, the cathode of the high intensity light source may be elongated and may be in the form of a portion of a cylindrical surface. The screen of the resulting cathode ray tube would also be elongated and generally coextensive with the cathode. It is also contemplated that the present light source may be used in systems where intense brief pulses of light are desired, other than of the photographic type shown in FIG. 2. Accordingly, it is to be understood that the present invention is to be limited by'the spirit and scope of the appended claims.

What is claimed is:

l. A broad area strobe type light source comprising a cathode ray tube having a faceplate of at least six square centimeters surface area, a phosphor coating on the innor surface of said faceplate having a persistency which is less than 50 nanoseconds for decay to the one-half brightness point, means includinga broad area concave cathode for supplying an electron beam having a density of at least 5 amperes per square centimeter simultaneously to the entire surface area of said coating, a grid located between said cathode and said faceplate immediately ad jacent said cathode, means for protecting the coating from the intense heat of said cathode, a thin conductive coating on the inner surface of said phosphor coating, an anode structure electrically coupled to said conductive coating, means for applying a potential of at least 10 kilovolts to said anode structure, means for normally biasing said grid to a negative potential, and means for applying brief positive gating pulses to said grid, said pulses having a duration of less than one-half microsecond.

2. In combination, a cathode ray tube having a phosphor screen With an area of at least six square centimeters and means for supplying an electron beam having a density of at least 5 amperes per square centimeter simultaneously to the entire surface area of said screen.

3. A broad area strobe type light source comprising a cathode ray tube having a screen of at least six square centimeters surface area, means including a concave cathode having br-oad surface area comp-arable to that of said screen for sup-plying an electron beam having a density of at least 5 amperes per square centimeter to said screen, a grid located between said cathode and said screen immediately adjacent said cathode, means for protecting the screen from the intense heat of said cathode, a phosphor coating on said screen having a persistency which is less than 50 nanoseconds for decay to the one-half brightness point, a thin conducting coating on the inner surface of said screen, an elongated conductive anode structure electrically coupled to said conducting coating and extending from said coating toward said grid, means for applying a potential of at least kilovolts to said anode structure, corona rings located on the surfaces of said grid and anode adjacent other electrodes to avoid sparking, means for normally biasing said grid .to a negative potential, and means for applying brief positive gating pulses to said grid, said pulses having a duration of less than one-half microsecond.

4. A broad area strobe type light source comp-rising a cathode ray tube having a phosphor screen of at least six square centimeters surface area, said phosphor screen having a persistency which is less than 50 nanoseconds for decay to the one-half brightness point, means including a cathode having a broad area comparable in extent to that of said screen for supplying an electron beam having a density of at least 5 amperes per square centimeter to said screen, a grid located between said cathode and said screen immediately adjacent said cathode, means for protecting the screen from the intense heat of said cathode, a thin conducting coating on the inner surface of said phosphor screen, an anode structure electrically coupled to said conducting coating; means for applying a potential of at least 10 kilovol-ts to said anode structure, means for normally biasing said grid to a negative potential, and means for applying brief positive gating pulses to said grid, said pulses having a duration of less than one-half microsecond.

5. A broad area strobe type light source comprising a cathode ray tube having a phosphor screen of at least six square centimeters surface area, said phosphor screen having a persistency which is less than 50 nanoseconds for decay to the one-half brightness point and having a predetermined spectral output characteristic, means ineluding a cathode having a broad area comparable in extent to that of said screen for supplying an electron beam having a density of at least 5 amperes per square centimeter to said screen, a grid located between said cathode and said screen immediately adjacent said cathode, means tor protecting the screen from the intense heat of said cathode, a thin conducting coating on the inner surface of said phosphor screen, an anode structure electrically coupled to said conducting coating; means for applying a potential of at least 10 kilovolts to said anode structure, means for normally biasing said grid to a negative po tential, means for applying brief positive gating pulses to said grid, said pulses having a duration of less than onehalf microsecond, and a photographic system having a spectral response characteristic corresponding substantially to said spectral characteristic of said phosphor screen mounted to receive light from said screen.

References Cited by the Examiner UNITED STATES PATENTS 2,133,138 10/38 Hamac-her 313-187 X 2,698,914 1/55 Tryon 315-30 2,898,492 8/59 Miller 31374 2,986,668 5/61 H'aflinger et a1. 3l385 2,992,347 7/6 1 Dehn 31382 OTHER REFERENCES Zworvkin et al.: Television, John Wiley and Sons, New York, 1940, pp, 360-36 2.

ZWoryk-in et al.: Television, John Wiley and Sons, New York, 1954, 2nd edition, pp. 437-439.

DAVID G. REDINBAUGH, Primary Examiner.

RALPH G. NILSON, ROY LAKE, Examiners. 

1. A BROAD AREA STROBE TYPE LIGHT SOURCE COMPRISING A CATHODE RAY TUBE HAVING A FACEPLATE OF AT LEAST SIX SQUARE CENTIMETERS SURFACE AREA, A PHOSPHOR COATING ON THE INNER SURFACE OF SAID FACEPLATE HAVING A PERSISTENCY WHICH IS LESS THAN 50 NANOSECONDS FOR DECAY TO THE ONE-HALF BRIGHTNESS POINT, MEANS INCLUDING A BROAD AREA CONCAVE CATHODE FOR SUPPLYING AN ELECTRON BEAM HAVING A DENSITY OF AT LEAST 5 AMPERES PER SQUARE CENTIMETER SIMULTANEOUSLY TO THE ENTIRE SURFACE AREA OF SAID COATING, A GRID LOCATED BETWEEN SAID CATHODE AND SAID FACEPLATE IMMEDIATELY ADJACENT SAID CATHODE, MEANS FOR PROTECTING THE COATING FROM THE INTENSE HEAT OF SAID CATHODE, A THIN CONDUCTIVE COATING ON THE INNER SURFACE OF SAID PHOSPHOR COATING, AN ANODE STRUCTURE ELECTRICALLY COUPLED TO SAID CONDUCTIVE COATING, MEANS FOR APPLYING A POTENTIAL OF AT LEAST 10 KILOVOLTS TO SAID ANODE STRUCTURE, MEANS FOR NORMALLY BIASING SAID GRID TO A NEGATIVE POTENTIAL, AND MEANS FOR APPLYING BRIEF POSITIVE GATING PULSES TO SAID GRID, SAID PLUSES HAVING A DURATION OF LESS THAN ONE-HALF MICROSECOND. 